Prepare the broth by adding the cold water to a saucepan with kelp. Bring the kelp up to a boil, then let it gently simmer for 5 minutes

Remove from the heat and add in the bonito flakes and let sit for 5 minutes

Strain the kelp and bonito flakes from the broth and place the broth back over a low heat

Add the thinly sliced shiitake mushrooms and chopped fish to the hot broth and allow them to cook for the next 3-5 minutes

Season with salt and pepper to taste